1. Field of the Invention
The present invention relates a moving body system including a linear motor having a primary side on the ground and a secondary side on a moving body. In particular, the present invention relates to a technique of measuring an initial position of the moving body, e.g., at the time of a start-up operation of the system.
2. Description of the Related Art
JP2007-82307A discloses a technique of controlling a linear motor by providing a movable element of the linear motor on a moving body such as a stacker crane, providing stationary elements of the linear motor on the ground, and detecting a position of the moving body using linear sensors. The stationary elements are provided discretely, and the linear sensors are provided discretely to determine the position of the moving body based on a signal from a linear sensor detecting the moving body.
In this regard, in general, the movable element is made up of a plurality of magnets, and the linear sensor determines the position of a detected magnet among the plurality of magnets by counting the number of magnets. For determining the position of the movable element without counting the number of magnets, a linear sensor having a measurement range longer than the length of the movable element is required. Such a linear sensor is disadvantageous in terms of the cost. For example, at the time of performing a starting operation of a system for the first time, or at the time of performing a restoring operation after a power failure, it is necessary to carry out the start-up operation of the system from a state where the initial position of the moving body is unknown. In the case of using a position sensor having a measurement range that is shorter than the length of the movable element, at the time of the start-up operation, the position of the movable element cannot be determined unambiguously. Under the circumstances, there is a demand to unambiguously determine the position of the movable element at the time of start-up operation, even in the case of using a position sensor having a measurement range that is shorter than the length of the movable element.